I'm probably the biggest Castellanos critic on here. I never would have signed him let alone kept him this long on the roster. However, when Harper got injured and could no longer play RF, Castellanos gave us an option.
Is it a great option? No, especially defensively he is bad with a dWAR of -6.1 during his time here in PHL. His oWAR during that time is 6.1 which has helped when he is hot, but not so much during his cold spells of chasing pitches and getting himself out. His oRAR is 65.
Sosa, during his time here, has posted a dWAR of 1.3 almost exclusively as a 2B, 3B or SS. That is how they see him, as an IF bench/defensive replacement/spot starter guy. His oWAR during that time is 3.7 and his oRAR is 38.
I have wanted a RF upgrade for Castellanos for several years and the best defensive OF lineup for us is Marsh, Rojas and Kepler, but we have multiple platoon guys, the Phillies like Nick's offense and his contract is a sunken cost they want to get something for in return. Castellanos is not a bench player, does not have the attitude or versatility for that role. Sosa has both and why the Phillies like him in that role.
I'm hoping that we will finally move Castellanos along after this season and find a real upgrade, but looking at the Phillies payroll and reported interest in bringing back both Schwarber & Realmuto, it likely is a pipe dream to land a Tucker or similar talent for RF. Sosa is not that guy.